The subject matter disclosed herein relates generally to a light sensor in a gamma ray detector, and more particularly, to systems and methods for signal path lengths for micro-cells of the light sensor.
Gamma ray detectors may be used in different applications, such as in Positron Emission Tomography (PET) systems. PET systems perform nuclear medicine imaging that generates a three-dimensional image or picture of functional processes within a body. For example, a PET system generates images that represent the distribution of positron-emitting nuclides within the body of a patient. When a positron interacts with an electron by annihilation, the entire mass of the positron-electron pair is converted into two 511 keV photons. The photons are emitted in opposite directions along a line of response. The annihilation photons are detected by detectors that are placed along the line of response on a detector ring. When these photons arrive and are detected at the detector elements at the same time, this is referred to as coincidence. An image is then generated based on the acquired image data that includes the annihilation photon detection information.
In silicon photomultiplier (SIPM) based PET detectors, in order to cover a large area for detection of gamma rays, a large number of small area SIPM (e.g., 3×3 mm2 or 4×4 mm2 photomultiplier devices) are grouped to form pixel device. The SIPM is formed by a micro-cell array. Each microcell contains avalanche photo diode and quenching circuitry (e.g. quenching resistor). When a bias voltage applied to APD is above breakdown and a micro-cell detects a photon, the APD capacitance discharges to a breakdown voltage and recharging current creates a signal by a signal path and received by a pin-out which is measured by the PET system. The timing performance of the SIPM is affected by the transmit time from the micro-cell, after detecting the photon, to the pin-out. The timing performance of the SIPM is important for the PET system to accurately determine the coincidence and corresponding image data as well as the timing resolution of the PET system. Conventional SIPM's are formed using rectangular micro-cells, requiring a signal path that includes 90 degree or orthogonal “zig-zags.” However, signal paths with orthogonal “zig-zags” increases the path length of traces reducing the timing performance of the SIPM.